Our objectives are: 1) detailed studies of the structure and function of biological membranes and 2) the development and application of new chemical and physical methods for ultrastructure studies. In the first category, experiments will be carried out to elucidate the mechanisms of trans-membrane linkage between surface receptors and actomyosin components underneath the cell surface. In studies with normal fibroblasts in monolayer culture, the immobilization of surface receptors by linkage to extended actomyosin filaments inside the cell will be further investigated. Likewise, the attachment of surface receptors to actomyosin proteins during receptor capping on lymphocytes and other cells in suspension, will be further analyzed. The possible involvement of products of the major histocompatibility gene complex in these linkage phenomena will be explored. Whether specific cell-cell interactions involve a mutual capping of the two cells will also be investigated by immunofluorescent techniques developed in our laboratory. In the second category, we will continue to develop methods to study intracellular interactions by double-labeling methods in immunofluorescence and immunoelectron microscopy.